1. Technical Field
The present invention relates to an impact absorber that absorbs an impact at the time of a collision or the like, and relates to an impact absorber suitably used in, e.g., an automobile.
2. Related Art
An impact absorber that is mounted on, e.g., an automobile and absorbs an impact from the outside is conventionally known. In the impact absorber, an energy absorbing member formed in, e.g., a tubular shape receives an impact load and is longitudinally crushed, whereby the energy absorbing member absorbs the impact load (impact energy). Conventionally, an energy absorbing member made of a metal (e.g., aluminum alloy) is used as the energy absorbing member. However, in recent years, an energy absorbing member made of a composite material (e.g., fiber reinforced plastic) that has higher energy absorption performance and is lighter is developed and is becoming commercially practical.
Incidentally, in such an impact absorber, the elastic modulus of the energy absorbing member significantly influences the energy absorption performance.
For example, Japanese Unexamined Patent Application Publication (JP-A) No. H6-300068 proposes an energy absorbing member formed of a composite material having a layer structure in which a reinforced fiber having a high strength is used in an inner layer and a reinforced fiber having a high elastic modulus is used in an outer layer. According to the energy absorbing member described in JP-A No. H6-300068, it is possible to obtain excellent energy absorption performance such as a high resistance before a rupture occurs, stable energy absorption after the rupture, and a high strength against buckling.
However, in the energy absorbing member in which the reinforced fiber having a high strength (or a high elastic modulus) is used in the inner layer, in the case where the inner layer has received a load first, the energy absorbing member bears a large load while hardly being displaced in a crush direction. More specifically, in such a case, as illustrated in FIG. 5, the energy absorbing member displays a load-displacement characteristic having an uneven rise in which the peak of the load leading to the rupture of the inner layer is seen in an initial stage. Thus, in the case where the rise of the load-displacement characteristic is not smooth, there is a possibility that deterioration of an injury of a passenger resulting from a secondary collision or the like is caused.